The present invention concerns rock crushers and particularly impact crushers of the vertical shaft type.
As is well known, the anvils in a vertical shaft impact crusher wear at a rate second only to the impeller shoes and so must also be replaced at periodic intervals. Typically the anvils are carried by an anvil ring seated within the upper end of the crusher housing or "tub", as it is often called. But fine and coarse rock, angular and sharp edged from fracturing, accumulates on top and behind the anvils and the anvil ring. So densely packed does the accumulation become that removal of the anvils and the anvil ring is both difficult and time consuming. After removing the crusher lid it often needs two men with hammers and bars up to one hour to chip away the accumulation before the ring and anvils can be detached. Even a single rock can bar removal of the anvil ring.
Not only must the anvils be replaced when worn out but for economy's sake they must also be rotated. As is likewise well known, the anvils wear unevenly, those in one sector abrading the least, the wear on the remaining anvils graduating between the two extremes. It is not uncommon to have a 30% to 50% difference between the most and least worn anvils. The reason for this, as will be explained more fully later on, has to do with the nature of the feed tube carried by the crusher lid, as well as with the direction of the feed into the hopper from the conveyor. Usually the crusher operator first replaces the most worn anvils, after having excavated the accumulation of rock above them as previously described. Some anvils will have remaining wear life but often the operator will also replace those anyway rather than endure the down time involved in replacing them a few days later. There is then not only a mismatch, unworn and worn anvils in the crusher, but it is most difficult afterwards, until a complete set of new anvils is installed, to arrange anvil replacement in order that all anvils are equally worn before they are discarded. This is because the next anvils needing replacement are among those of graduated wear between the most and least worn, again causing a mismatch. When the least worn at last must be discarded there is approximately 30% to 50% wear on those which first replaced the most worn anvils. At this time it is common to exchange the least worn anvils for the most worn ones either by moving them individually or by rotating the anvil ring 180.degree.. But however rotation of the anvils is performed in current practice, manual labor is required to knock out the accumulated rock above. Even then it is often still difficult or impossible as a practical matter either to rotate the anvil ring in place or to remove it for rotation because of liming, corrosion and the like between the anvil ring and the tub in which the ring is seated. Hence, in most cases the anvils must be individually removed from the anvil ring and replaced 180.degree. from their previous location.
Accordingly, the primary object of the invention is the provision of a vertical impact crusher in which the anvils can be replaced and/or the anvil ring and anvils as a unit easily rotated to even out anvil wear, all with a minimum of time and labor.